(1) Field of the Invention
This invention relates in general to the manufacture of thick film microcircuits and more particularly to a method producing fine line conductive/resistive patterns on an electrically insulating coating.
(2) Description of the Prior Art
Thick film microcircuits requiring high density circuit packaging and compatability with integrated circuit leads require circuit patterns with conductive elements as small as 2 mils wide (0.002 inch). The conventional method of screen printing thick film patterns on a film substrate cannot consistently produce patterns with element widths less than 5 to 10 mils. Photolithographic techniques have been used to produce thick film patterns with 2 mil wide conductors, but the process is somewhat complicated and costly.
The conventional method used to produce thick film circuit patterns is to apply conductive and/or resistive "inks" onto a ceramic substrate through a prepared pattern on a wire mesh or stencil. The deposited ink pattern and substrate are "fired" in a furnace to remove the solvents from the paste and sinter the material to the ceramic base. The reproduction of fine images on a screen or stencil is difficult to achieve compounded by the tendency for thick film paste to "slump" or run after it has been printed. These two conditions combine to limit the practical minimal width and spacing of the printed elements on film circuits to 5 to 10 mils.